There has conventionally been used a honeycomb structure made of ceramic as a filter for trapping particulate matter in exhaust gas from an automobile, in particular, diesel particulate matter (DPF: Diesel Particulate Filter) or as a catalyst carrier for loading a catalyst for purifying nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbon (HC), etc., in exhaust gas. As such a honeycomb structure, for example, as shown in FIGS. 14 to 17, there has been proposed a honeycomb structure 51 provided with a cell structure 52 (also referred to as a cell structural portion) and an outer peripheral coat layer 53 (also referred to as an outer peripheral coat portion) disposed on the outer peripheral face of the cell structure 52 (see, for example, Patent Documents 1 and 2).
Such a conventional honeycomb structure 51 is constituted in such a manner that an end portion of the outer peripheral coat layer 53 is at the same level as an end face of the cell structure 52. Here, FIG. 14 is a perspective view schematically showing a conventional honeycomb structure, FIG. 15 is a plan view showing an end face of the honeycomb structure shown in FIG. 14, FIG. 16 is a B-B line cross-sectional view in FIG. 14, and FIG. 17 is a partially enlarged view of the end face shown in FIG. 15.
Such a honeycomb structure 51 is incorporated in an exhaust gas system of a diesel engine or the like by a canning technique using a holding member in order to trap and remove particulate matter contained in exhaust gas from, for example, a diesel engine. For example, as shown in FIG. 18, the outer peripheral face of the honeycomb structure 51 is covered with a heat resistant holding member 66 having compressive elasticity such as a wire mesh mat and put in a metal container 67 (converter container) with applying compressive surface pressure via the holding member 66.
At this time, a retainer ring 69 is disposed in the outer peripheral portion of the honeycomb structure 51 lest the honeycomb structure 51 should have displacement due to, for example, pressure of the exhaust gas or vibrations of the engine to keep the honeycomb structure 51 in the metal container 67. Here, FIG. 18 is a cross-sectional view including the central axis and schematically showing an example of a state where a conventional honeycomb structure is fixed in a cylindrical metal container. Incidentally, the reference numeral 70 denotes a gas seal.
In addition, as shown in FIG. 19, there is another example where an outer peripheral face of the honeycomb structure 51 is covered with a holding member 58 such as a ceramic mat having gas sealability instead of disposing the retainer ring 69 (see FIG. 18) to put the honeycomb structure 51 in the metal container 67 with applying surface pressure to incorporate the honeycomb structure 51 into an exhaust gas system of a diesel engine or the like. Here, FIG. 19 is a cross-sectional view including the central axis and schematically showing another example of a state where a conventional honeycomb structure is fixed in a cylindrical metal container.
Patent Document 1: JP-A-H5-269388
Patent Document 2: JP-A-H3-275309